The present invention relates generally to an ultrasonic phased array transducer and more particularly to an ultrasonic phased array. transducer having an ultralow impedance backfill and a method for making.
A typical ultrasonic phased array transducer used in medical and industrial applications includes one or more piezoelectric elements placed between a pair of electrodes. The electrodes are connected to a voltage source. When a voltage is applied, the piezoelectric elements are excited at a frequency corresponding to the applied is voltage. As a result, the piezoelectric element emits an ultrasonic beam of energy into a media that it is coupled to at frequencies corresponding to the convolution of the transducer""s electrical/acoustical transfer function and the excitation pulse. Conversely, when an echo of the ultrasonic beam strikes the piezoelectric elements, each element produces a corresponding voltage across its electrodes.
In addition, the ultrasonic phased array typically includes acoustic matching layers coupled to the piezoelectric elements. The acoustic matching layers transform the acoustic impedance of the patient or object to a value closer to that of the piezoelectric element. This improves the efficiency of sound transmission to the patient/object and increases the bandwidth over which sound energy is transmitted. Also, the ultrasonic phased array includes an acoustic backing layer (i.e., a backfill) coupled to the piezoelectric elements opposite to the acoustic matching layers. The backfill has a lower impedance than the piezoelectric elements in order to direct more of the ultrasonic beam towards the patient/object rather than the backfill. Typically, the backfill is made from a thick, lossy material that provides high attenuation for diminishing reverberations of the sound frequencies involved. As an echo of sound waves goes to or returns from the patient/object some of the waves will escape into the backfill material and may interfere with other echoes returning from the patient/object. However, most of these sound waves are attenuated greatly by the thick, lossy, backfill material so that returned echoes from the backfill are unimportant.
However, a problem with using a thick, lossy, backfill with an ultrasonic phased array transducer is that it is difficult to achieve electrical and acoustical isolation by separating the array of piezoelectric elements with independent electrical connections. Typically, the piezoelectric elements are separated by using a dicing saw, a kerf saw, or by laser machining. Electrical connections made through the backfill layer must not interfere with the other acoustic properties (i.e. high isolation, high attenuation, and backfill impedance). In certain applications such as 1.5 or 2 dimensional arrays, there is a very small profile which makes it extremely difficult to make electrical connections without interfering with the acoustic properties of the ultrasonic phased array.
One approach that has been used to overcome this interconnect problem is to bond wires or flexible circuit boards to the piezoelectric elements. However, these schemes are difficult to implement with very small piezoelectric elements or in 2 dimensional (2-D) arrays, since backfill properties or acoustic isolation may be compromised. An example of a handwiring scheme that is not practicable for commercial manufacturing is disclosed in Kojima, Matrix Array Transducer and Flexible Matrix Array Transducer, IEEE ULTRASONICS, 1986, pp. 649-654. An example of another scheme that has been disclosed in Pappalardo, Hybrid Linear and Matrix Acoustic Arrays, ULTRASONICS, March 1981, pp. 81-86, is to stack individual lines of arrays of piezoelectric elements including the backfill. However, the scheme disclosed in Pappalardo is deficient because there is poor dimensional control. In Smith et al., Two Dimensional Arrays for Medical Ultrasound, ULTRASONIC IMAGING, vol. 14, pp. 213-233 (1992), a scheme has been disclosed which uses epoxy wiring guides with conducting epoxy and wire conductors. However, the scheme disclosed in Smith et al. is deficient because it suffers from poor manufacturability and acoustic properties. Also, a three dimensional (3-D) ceramic interconnect structure based multi-layer ceramic technology developed for semiconductor integrated circuits has been disclosed in Smith et al., Two Dimensional Array Transducer Using Hybrid Connection Technology, IEEE ULTRASONICS SYMPOSIUM, 1992, pp. 555-558. This scheme also suffers from poor manufacturability and acoustic properties.
Thus, there is a need for a backfill that can be used in an ultrasonic phased array transducer such that electrical and acoustical isolation of the array of piezoelectric elements can be maintained without interfering with their electrical and acoustical properties.
Therefore, it is a primary objective of the present invention to provide an ultrasonic phased array transducer having a backfill with an ultralow impedance that is made from aerogels, carbon aerogels, xerogels, or carbon xerogels, eliminating the need for a thick, lossy, backfill.
A second object of the present invention is to provide an ultrasonic phased array transducer with a backfill that can be electrically and acoustically isolated without interfering with the electrical and acoustical properties of the array.
Thus, in accordance with the present invention, there is provided an ultrasonic phased array transducer and a method for making. In the present invention, a low density backfill material having an ultralow acoustic impedance is bonded to a piezoelectric ceramic material and a plurality of matching layers. Portions of the bonded plurality of matching layers, the piezoelectric ceramic material, and the backfill material are cut therethrough to form an array of electrically and acoustically isolated individual elements.
In accordance with a first embodiment of the present invention, there is provided an ultrasonic phased array transducer and a method for making. In the first embodiment, there is a low density backfill material having an ultralow acoustic impedance. A flexible circuit board is bonded at one end of the ultralow impedance backfill. A piezoelectric ceramic material and a plurality of matching layers are bonded to the flexible circuit board and the backfill material, wherein the flexible circuit board is bonded between the backfill material and the piezoelectric ceramic material. A portion of the bonded plurality of matching layers, the piezoelectric ceramic material, the flexible circuit board, and the backfill material are cut to form an array of electrically and acoustically isolated individual elements.
In accordance with a second embodiment of the present invention, there is provided an ultrasonic phased array transducer and a method for making. In the second embodiment, there is a low density backfill material having an ultralow acoustic impedance. A piezoelectric ceramic material and a plurality of matching layers are bonded to the backfill material. A plurality of interconnect vias are formed in the backfill material. A conducting material is then deposited in the plurality of interconnect vias. Portions of the bonded plurality of matching layers, the piezoelectric ceramic material, and the backfill material are cut to form an array of electrically and acoustically isolated individual elements.
In accordance with another embodiment of the present invention, there is provided an ultrasonic phased array transducer and a method for making. In the third embodiment, there is an electrically conductive low density backfill material having an ultralow acoustic impedance. A piezoelectric ceramic material and a plurality of matching layers are bonded to the backfill material. An electronic layer is bonded to the backfill material at a face opposite to the bonded piezoelectric ceramic material and plurality of matching layers. The electronic layer is used for making electrical contacts to the piezoelectric ceramic material and to external devices. Portions of the bonded plurality of matching layers, the piezoelectric ceramic material, and the backfill material are cut to form an array of electrically and acoustically isolated individual elements.
In accordance with still another embodiment of the present invention, there is provided an ultrasonic phased array transducer and a method for making. In the fourth embodiment, a piezoelectric ceramic material and a plurality of matching layers are bonded on a substrate. The bonded plurality of matching layers and the piezoelectric ceramic material are cut to form an array of electrically and acoustically isolated individual elements. A low density backfill material having an ultralow acoustic impedance is deposited over the array of electrically and acoustically isolated individual elements. Next, a plurality of interconnect vias are formed in the backfill material and deposited with a conducting material in the plurality of interconnect vias.
While the present invention will hereinafter be described in connection with an illustrative embodiment and method of use, it will be understood that it is not intended to limit the invention to this embodiment. Instead, it is intended to cover all alternatives, modifications and equivalents as may be included within the spirit and scope of the present invention as defined by the appended claims.